i. Field of the Invention
This invention relates to sulphur cements and concretes produced therefrom, and to processes for the preparation thereof.
ii. Description of the Prior Art
Sulphur cements have a long history of use in specialized applications. Thus, Canadian Pat. No. 71,686 issued to George McKay provided a sulphur-containing composition useful for sealing purposes at a joint, for roofing purposes, for the forming of ornamental figures, and for the coating of the exposed surfaces of iron or steel steps, the composition including sulphur, brick-dust, tin, lead, bismuth, plaster of paris and borax.
However, attempts to make durable, high strength concrete-like materials from sulphur cements have encountered cost, durability, or other difficulties that precluded commercialization. Proposals have been made to increase the strength of sulphur as a bonding agent by the addition of coal, sand or pumice thereto. Moreover peculiar characteristics were proposed to be imparted by the addition thereto of bitumens, metallic sulphides, and fibrous materials. Also U.S. Pat. No. 3,459,717 patented Aug. 5, 1969 by J. B. Signouret, provided a sulphur-based plastic composition of improved fireproofing characteristics by the incorporation, into the molten sulphur, of a diester of dithiophosphoric acid and an ethylenic hydrocarbon. A major problem in the commercialization of sulphur cements has been the progressive embrittlement and subsequent crumbling, under thermal stress, of the sulphur cement. The cause of this embrittlement is believed to be the progressive crystallization of the initially amorphous sulphur. Partial inhibition of the crystallization has been achieved through various organic and inorganic additives.
Thiokol products (olefin polysulphides) have been used to stabilize the amorphous form of sulphur in sulphur cements. Thus, Canadian Pat. No. 356,181 issued Feb. 25, 1936 to W. W. Duecker, purports to provide a solution to the problem by dissolving, in the sulphur, certain olefin polysulphides or polymerization products thereof. These cements, however, were not practical on a large scale due to their high cost and disagreeable odor. Dicyclopentadiene has good stabilization properties and more favourable economics, but imparts a nauseating odor to the sulphur cement and has other shortcomings, e.g., its vapour, even at low concentrations, is highly toxic (see, for example, Kinkead et al, "The Mammalian Toxicity of Dicyclopentadiene." Toxicology and Applied Pharmacology, 20 552-561 (1971)). Moreover, dicyclopentadiene requires refluxing with molten sulphur to avoid excessive loss of material in vapour form.